Comment 70 for bug 1866870

David: Indeed ! How stupid I am. I missed the root cause inside QUEMU log file. This was clear enough...
error: kvm run failed Device or resource busy
This is probably because your SMT is enabled.

So I switch SMT (Power Simultaneous Multi-Threading) off and now it's OK; VMs are running and installing.

It had been years since I last touched KVM on Power and I lost my reflexes.
So please forget my precedent comment telling I had the same issue on Power platform. It was similar symptoms but not the same problem.